1. Field of the Invention
The present invention relates to an optical head device used in a reproducing apparatus and a recording apparatus of an optical data recording medium.
2. Description of the Related Art
The development of the optical head device, which is used in the reproducing apparatus and the recording apparatus of the optical data recording medium, has been actively performed in accordance with the development of the optical recording medium such as an optical disk and an optical magnetic disk. The feature of the optical head device lies in high recording density. More specifically, an optical beam is reduced to an optical spot having a size of about 1.mu. to be applied to the recording medium. Then, data is recorded in the recording medium or data, which is already read, is read. Whereby, the above feature can be realized.
An optical data recording system which can realize such a high recording density is characterized in that the distance between tracks of the recording medium in which data is recorded is narrower than a magnetic recording system. Due to this, there is needed a controlling method for irradiating the narrow recording track with the optical beam. Generally, in order to realize such control, there is required performance for maintaining a natural frequency band to 10 kH to 40 kH in the optical head device. In order to realize such performance, various contrivances have been made to improve an oscillation characteristic of a driving system.
The following will explain the prior art of the optical head device.
FIGS. 1 and 2 are a plain view and a cross sectional view showing the optical head device of the prior art.
In the figures, reference numeral 100 is an objective lens, which is attached to a cylindrical movable member 101. The movable member 101 is provided so as to be rotatable around a shaft 102 extending in a perpendicular direction of an optical disk (not shown) and movable in a longitudinal direction of the shaft 102 in parallel. One end of the shaft 102 is secured to a carriage 103. A slide bearing is provided at two portions of the carriage 103. Since guide rails 105a and 105b are inserted to the slide bearing 104, the carriage 103 can be straight moved. The carriage 103 is supported to be movable from the innermost periphery of the optical recording medium (optical disk) (not shown) to the outermost periphery.
A focusing coil 107 and a tracking coil 108 are adhered to a side surface of the movable member 101. The focusing coil 107 and the tracking coil 108 are formed such that a magnetic filed is provided thereto by a magnetic circuit 109 provided on the carriage 103. Then, a current is made to flow to the focusing coil 107, so that the movable member 101 is moved in a focusing direction, i.e., an optical direction of the objective lens 100. Also, a current is made to flow to the tracking coil 108, so that the movable member 101 is moved to be rotatable around the shaft 102 and the objective lens 100 is slightly moved in the tracking direction.
Moreover, linear motor coil 110a and 110b are attached to both side surfaces of the carriage 103. Linear motor magnetic circuits 111a and 111b are provided on a base (not shown) to provide a magnetic filed to the linear motor coils 110a and 110b. A current is made to flow to the linear motor coils 110a and 110b, so that the carriage 103 is largely moved, and the entire moving body including the objective lens 100 mounted on the carriage 103 can be moved to a place in the vicinity of a desired position of the optical disk.
However, in such a conventional optical head device, there was a problem as motioned below.
More specifically, since the magnetic circuit 109 including a permanent magnet, etc. was mounted on the carriage 103, mass of the entire moving body including the carriage 103 became relatively large. Due to this, acceleration of the carriage 103, which can be obtained by the linear motor coils 110a and 110b, was not always sufficient to realize a future high-speed seek.
In order to solve the above problem, several proposals have been made to reduce the number of parts of the moving body including the carriage. For example, Japanese Patent Application KOKAI Publication No. 5-205284 discloses an optical head device in which no magnetic circuit including the permanent magnet etc. is provided. In this case, the linear motor magnetic circuit, which is conventionally used as a large movement to the tracking direction, is also used as a slight movement. In other words, the large movement and the slight movement to the tracking direction can be realized by combining the linear motor magnetic circuit and the linear motor coils with each other. By this improvement, the reduction of mass of the entire moving body was able to be realized to some extent.
However, the reduction of mass, which is sufficient to obtain the high-speed seek, has not been realized yet. Also, oscillation in which unfavorable influence is exerted on the seek is generated in the movable member due to friction occurred at the time of movement. Moreover, in a case where a driving coil in the focusing direction is provided at both ends of the carriage, the coil is deformed at the time of movement. Due to this, oscillation is generated. As mentioned above, there is still left a problem to be solved.